This invention relates to an improved-efficiency welding device in a plastic bag production machine.
In welding machines for plastic bag production in general, a plastics material in tubular form is passed in a flattened state between at least one pair of calenders within a transverse welding unit. This transverse welding unit comprises essentially a heated upper welding bar and a heated lower welding bar which are brought into contact with the plastics material passing between them. One welding bar, for example the upper one, moves reciprocatingly in a vertical direction towards and away from the other welding bar.
Because of the high rate at which the machine usually operates, the upper welding bar strikes the plastics material and the lower welding bar with considerable impact, to the extent of even cutting or at least marking the material, with consequent deterioration or the plastics material. In addition, the high rate means that an optimum weld cannot be achieved because of the extremely short time for which the hot bar remains on the plastics material.